I'm in an ordinary house with a sloping double roof, covered only by fiber cement slates, which have always been waterproof for 53 years.
No insulation under the frame.
20cm glass wool above the living floor.
So a large attic, full to bursting, with bulky objects judiciously placed on the rafters.
In summers, we suffer from the heat when it hits during the day.
In fact, the attic with its buffer inertia from the bazaar, becomes a bread oven...
And at night it is painful.
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The green roof is not considered.
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I had thought about remedying it, in an original way (in my opinion), well over 30 years ago, without ever doing it because I was always looking for the best way to achieve it.
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It is simply a question of moistening the exterior roof, by variable interludes according to the temperature under the roof, and only, to avoid a 35° at night in the "habitable" /

In a discreet way, that is to say not demonstratively, in the necessary proportion.
No question of putting a turnstile there.
Nor to spray water from the ground on a roof 7m higher (two levels below), every 20 minutes.
I was thinking of installing a pipe with small holes of 1mm every 1cm, eg.
Placed just at the height of the roof in order to water the 2 slopes with holes at an angle of 70°.
Thus it will flow on the slopes, until the entire surface is wet, then stop on pause.
And evaporation will do its job to cool the surface.
I don't claim to cool the house like this, just prevent the attic from overheating like a bread oven, during “heat waves”.
Water is not a problem as I have a rainwater tank.
Of course we will criticize the expense of water, but it's just to be able to sleep in a room at less than 30°.
We just had a week, which reminded me of this problem, recurring in the summer and less bearable with age.
I think that this “wastage” for an outside view (and yet so useful for us) is much less than buying an air conditioning unit and supplying it with electricity all day… It's clear.
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For the realization, I was thinking of a copper pipe (over 13m), so that it remains permanent, but corrosion and verdigris on the holes? (It's still useful for mosses, but hey, it's been fine for half a century now)
But I fear for the weakening of the flow for the far holes.
I imagine that rather than feeding it in 2 places, to only make a water inlet in the middle of the 13m.
On 6,5 m the flow would remain correct?
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What do you think ?
And technical opinions and advice from knowledgeable do-it-yourselfers.
On the type of pipe.
If we shouldn't rather put one on each slope so as not to bother life, for the angulation of the holes.
And to avoid a possible adjustment, because my mobility on the roof, is not really there any more, to walk me briskly there.
This would allow them to be powered independently. Since the East-West slopes are exposed together only in the middle of the day.